PIM kinase family consists of three homologous serine/threonine kinases, Pim-1, Pim-2, and Pim-3, which belong to calmodulin-dependent protein kinase-related family (CAMK). Researches have shown that PIM kinases are widely expressed in hematopoietic tissues (J. Biol. Chem., 280, 14168-14176, 2005; Blood, 105, 4477-4483, 2005) and play important roles in cell survival and proliferation. Since PIM kinases are overexpressed in a variety of malignancies and inflammations (J. Exp. Med., 201, 259-266, 2005; Biochem. Soc. Trans., 32, 315-319, 2004), they are more and more being targeted for treating cancers and immune dysfunctions. PIM-1 (Provirus Integration of Maloney 1) was originally identified in a series of insertional mutagenesis studies of retroviruses, as a frequent proviral integration site in Moloney murine leukemia virus-induced T-cell lymphomas, and PIM-1 was named based on that finding (Cell, 37, 141-150, 1984). It was found later that the genes encoding PIM-2 (Provirus Integration of Maloney 2) have the same defect (J. Clin. Invest., 115, 2679-2688, 2005). Pim-2 has similar effects as and compensatory to Pim-1 (J EMBO, 14, 2536, 1995). PIM-3 was initially named as KID-1 (Kinase Induced by Depolarization 1), but renamed to Pim-3 because of its high sequence similarity to Pim-1 (Nature, 428, 332-337, 2005; Cell, 56, 673-682, 1989). PIM-1, 2, 3 are overly expressed in many hematopoietic malignancies (PNAS USA, 86, 8857-8861, 1989). PIM-1 was found to be overexpressed in the development of prostate cancer (J. Clin. Pathol., 59, 285-288, 2006). PIM-2 expression is elevated in human chronic lymphocytic leukemia and non-Hodgkin's lymphoma leukemia (Leuk. Lymph., 45, 951-955, 2004), the aberrant expression of PIM-3 is believed to have played an important role in the development and proliferation of live fibroma (Int. J. Cancer, 114, 209-218, 2005) and pancreatic cancer (Cancer Res., 66, 6741-6747, 2006).
PIM-1, 2, 3 have effects on the survival and proliferation of hematopoietic cells in response to growth factors stimulation. PIM-1, 2, 3 triple knockout mice are viable and fertile while displaying reduced body size and impairment of proliferation of hematopoietic cells in response to growth factors. Knocking out one of 3 kinases does not have obvious effect on mice, indicating some overlapping functions among PIM kinases (Cell, 56, 673-682, 1989). The substrates of PIM kinases include Bcl-2 family members such as pro-apoptotic BAD protein (FEBS Letters, 571, 43-49, 2004), cell cycle regulating p21 (Biochem. Biophys. Acta, 1593, 45-55, 2002), CDC25A, C-TA (J. Biol. Chem., 279, 48319-48328, 2004), protein synthesis related 4EBP1 (Blood, 105, 4477-4483, 2005). These functions of PIM kinases indicate that PIM kinases can prevent apoptosis and promote cell growth and proliferation. Their overexpression in cancer cells promotes the survival and proliferation of the cancer cells. Therefore, inhibiting the PIM kinase activities in cancer cell is a new effective way of treating cancers. Besides cancer, PIM inhibitors can also be used to treat autoimmune diseases, allergic reactions, and organ transplant rejection (Immunology, 116, 82-88, 2005).